Compression Molding – manufacturing process guide

Compression molding is one of the oldest and most widely used processes for the production of thermosetting plastic parts. Compression molding machines consist of platens to which the two halves of a mold is attached. The name given to the raw material used for the production of the parts is known as a charge.

A calculated amount of charge (which can be in the form of liquid, pellets or powder) is heated and then placed into the lower half of the mold.

Both halves of the mold are preheated. Then with the help of a hydraulic system the mold is closed, forming the material into the shape of the mold cavity.

The mold is left for some time so that polymerization can take place, converting the raw material into the solid final product.

Compression molding products

Materials for compression molding

Compression molding is mostly used for the production of thermosetting polymers, but other materials including elastomers, some composites and a limited range of thermoplastics can also be processed using this method.

Design Considerations

The process typically has a single plane mold, so the complexity level of the part geometry is limited.

Parts are limited to an area of 3 mm2 to 1.5 m2.

Section thickness is typically limited to between 0.8mm and 13mm.

Features like holes, ribs, lettering, threads and bosses can be added.

Process Variations

In compression molding there are three type of molds, used for the production of different types of parts: Flash type, Semi positive type, Positive type.

Shallow parts are manufactured using flash type molds. These produce a lot of waste material as flash, which requires post processing and flash removal.

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